Uniformed nanosized zeolites are important in many technical areas such as catalysis. Therefore, some examples are reported relating to the synthesis of these zeolites.
EP 1 195 368 A2 describes a process for the catalytic selective oxidation of a hydrocarbon compound in the presence of a mesoporous zeolite. As zeolite, a titanium containing zeolite, in particular a zeolite TS-1 is disclosed. It is described that, contrary to nanosized TS-1, separation of mesoporous TS-1 was found to be easily accomplished by simple filtration. The mesoporous zeolite is prepared by crystallisation in a mesoporous solid-state carbon matrix followed by removal of the matrix by combustion. This process necessarily leads to relatively large crystals, i.e. crystals having a size in the range from about 0.3 to 1.2 micrometer. Thus, crystals having a broad size distribution were obtained.
EP 1 331 032 A2 describes a process for preparing a catalytic material prepared by an immobilisation process in a non-crystallographic mesopore system, wherein mesoporosity is primarily introduced into the individual zeolite single crystal during crystallisation. Thus, a solid-state matrix is used for preparing the catalyst which does not allow for an easy change of the size of the crystals by varying a simple parameter of the process.
In “Colloidal Zeolite Suspensions”, Zeolites Vol 14 (1994) pages 110 to 116B. J. Schoeman et al, describe a process for producing discrete zeolite particles with an average particle size of less than 150 nm and a narrow particle size distribution. Key parameter of this process is the addition of sodium in the crystallisation process. Thus, this method is limited to zeolites which contain sodium or, in case the zeolite shall be used in a technical area where sodium is disadvantageous, the sodium has to be removed, if possible at all, from the zeolite in an additional post-treatment.
In “The Synthesis of Discrete Colloidal Particles of TPA-Silicate-1”, Zeolites Vol 14 (1994) pages 557 to 567, A. E. Persson describe discrete colloidal zeolite particles with an average size of less than 100 nm and a narrow particle size distribution. As factors influencing the particle size, high silica content in conjunction with high alkalinities were found. Thus, this process is restricted to silicalite zeolites having high silica content and, as already discussed above, high alkali metal content with its negative effects.
In “Low-Temperature Synthesis and Characterization of a Stable Colloidal TPA-Silicalite-1 Suspension”, Zeolites Vol 18 (1997) pages 379 to 386, R. W. Corkery et al. describe a microporous zeolite material with a narrow size distribution, obtained by conventional techniques. The main focus of this article is the preparation of stable colloidal solution containing the zeolite particles.
In “Synthesis of ZSM-5 Zeolite with Small Crystal Size and its Catalytic Performance for Ethylene Oligomerization”, Zeolites Vol 14 (1994) pages 643 to 649, M. Yamamura et al. describe zeolites having a specific Al:Si ratio and crystal sizes of 30 to 50 nm. These zeolites are obtained using conventional techniques, the factors influencing the crystal size being the Si:Al ratio and the OH:Si ratio.
In “Synthesis of Ultrafine Zeolite L”, Proceedings of the 9th International Zeolite Conference. Montreal 1992 (R. von Ballmoos, editor), Butterworth-Heinemann (1993), pages 297 to 304, Xianping Meng et al. describe zeolite L particles having a size of about 30 nm, synthesized under hydrothermal conditions in an initial K2O—Al2O3—SiO2—H2O mixture. The optimal ranges of the concentrations of these compounds are investigated. Zeolites having an average diameter from about 60 to 650 nm or an average size from 300 to 1000 nm are disclosed.
In “Synthesis and Characterization of High-Quality Zeolite LTA and FAU Single Nanocrystals”, Chem. Mater. 10 (1998) pages 1483 to 1486, Guangshan Zhu et al. describe the optimization of synthesis conditions to obtain crystals having a size of 50 nm or 80 nm. The crystal size is described to be dependent from the addition of NaCl instead of NaOH so that the alkalinity of the system is solely influenced by the tetramethylammonium hydroxide. Apart from this modification, this synthesis route follows conventional techniques.
In “Influence of Zeolite Particle Size on Selectivity During Fluid Catalytic Cracking”, Applied Catalysis 23 (1986) pages 69 to 80, K. Rajagopalan et al. describe cracking catalysts having small, medium, or large particle size in the range of, e.g., 0.15 to 0.38, 0.24 to 0.88, or 0.70 to 1.042 micrometer. Particles of all sizes were obtained using conventional techniques.
In “Catalytic Cracking of Gasoil”, Applied Catalysis 55 (1989) pages 65 to 74, M. A. Camblor et al. describe faujasite type Y zeolites with an average crystal size of 0.30 to 1.0 micrometer and a controlled crystal size distribution. No hint is given as to how to control the size distribution.
CA 2346892 A1 describes a process for the preparation of silica having micropores and mesopores. The pores are obtained by adding a polymer as sole pore forming agent to the reaction mixtures from which the silica crystals are obtained. The document is silent on crystal sizes, let alone a process in which a pore forming agent is used in combination with a polymer as size directing agent.
In “Confined Space Synthesis. A Novel Route to Nanosized Zeolites”, Inorg. Chem. 39 (2000) pages 2279 to 2283, I. Schmidt et al. disclose a crystallisation of a zeolitic material inside the pore system of an inert mesoporous (soild-state) matrix. By proper choice of the matrix, it is described to be possible to control the size distribution of the zeolite. Carbon black was employed as matrix. Since solid-state matrices are described, the process lacks an easy control tool for influencing the size and size distribution of the zeolite since, in order to obtain a specific material, an adequate matrix has to be found or even newly synthesized.
Therefore, this prior art relates to controlling the crystal size and crystal size distribution, respectively, by adjusting the conventional synthesis gel composition, crystallisation time and/or temperature or by using the pore system an inert mesoporous matrix. However, these adjustments are comparatively complex.
Thus, it was an object of the present invention to provide a simple route for a size controlled synthesis of a nanosized zeolitic material having a narrow crystal size distribution.
In a scientific abstract by the inventor, published on the occasion of the 14th International Zeolite Conference, South Africa, Apr. 23–25, 2004, under the title “Synthesis of Uniformed Nanosized Zeolites from Reaction Gels inside Confined Polymer Spheroidal Voids”, the concept of synthesizing nanosized zeolites with the size of 200 to 300 nm from reaction gels was presented. It was disclosed that zeolite TS-1, zeolite ZSM-5, and zeolite beta can be prepared in the presence of spheroidal polymer acrylates. However, the document is completely silent on the chemical nature of those polyacrylates as well as their concentrations to be used for the synthesis of those zeolites. Additionally, this abstract explicitly discloses that the crystal nanosize of the zeolites can be designed and controlled by the choice of various polymer spheroidals. Consequently, the abstract teaches that controlling the size of the crystals is achieved by varying the polyacrylate used during synthesis. Therefore, it is disclosed that only chemically different polyacrylates lead to different crystal sizes. Nothing is disclosed regarding specific values of crystal size distributions.
Therefore, it is an object of the present invention to provide a novel process for preparing a nanosized zeolitic material which has a narrow crystal size distribution.
It is a further object of the present invention to provide a process for preparing a nanosized zeolitic material which allows for preparing the material in a comparatively large range of crystal sizes where for each crystal size of a given material, a narrow size distribution is assured.
It is still another object of the present invention to provide a process for easily controlling the size of the crystals of a given nanosized zeolitic material whereby for each size, a narrow crystal size distribution is assured.
It is another object of the present invention to provide the nanosized zeolitic material as such, the material having a specific narrow particle size distribution.
It is yet another object of the present invention to provide the nanosized zeolitic material as such, the material having micropores, having essentially no mesopores and having a specific narrow crystal size distribution.